1. Field of the Invention
The present invention relates to a multi-input multi-output system and a method for demodulating a transmitting vector in a receiver of the system in which the receiver detects a transmitting vector from a received vector received via multiple antennas and demodulates the detected transmitting vector.
2. Discussion of Related Art
A radio channel having a multi-path is known to have high channel capacity, and it is expected that multi-input multi-output (MIMO) systems will be widely used in the future. In an MIMO system, proper space-time processing provides ample multi-path scattering on a communication channel, as is already known.
The Diagonal-Bell Labs Layered Space-Time (D-BLAST) system was introduced by Foschini in 1996. Here, when several antennas for a transmitter and a receiver and a diagonal arrangement of codes are used for communication, respective code blocks are propagated while being diagonally crossed in time and space. In this case, if a channel environment is a Rayleigh scattering environment and a transmitter and a receiver have the same number of antennas, a transfer rate linearly increases with the number of antennas, eventually approaching 90% of Shannon's channel capacity. This system, however, is complex and thus difficult to implement.
Meanwhile, the Vertical-Bell Labs Layered Space-Time (V-BLAST) system was suggested by Wolniansky in 1998. This system simplifies a conventional D-BLAST system by means of hardware implementation, but cannot accomplish maximum diversity and thus has deteriorated performance.
FIG. 1 illustrates a schematic configuration of a conventional MIMO communication system using V-BLAST;
Referring to FIG. 1, a MIMO communication system using V-BLAST includes a transmitter 100 and a receiver 110.
The transmitter 100 includes a modulating unit 102 for modulating data to be transmitted using the same modulation system by applying the same modulation system to respective antennas, and the antennas for transmitting the modulated data via channels.
The receiver 110 includes antennas for receiving a vector r via the channels, a first multiplying unit 112 for multiplying the vector r received via the antennas by a Hermitian matrix Q, a decision feedback (DF) detecting unit 114 for performing decision feedback on a signal output from the first multiplying unit 112 to detect a transmitting vector therefrom, and a demodulating unit 116 for demodulating the transmitting vector output from the DF detecting unit 114 based on the system used for modulation at the modulating unit 102.
The DF detecting unit 114 detects a signal having the highest signal-to-noise ratio among the signals received via the transmitting antennas and detects the transmitting vector by removing previous-stage interference at each stage. The DF detecting unit 114 then inputs the detected transmitting vector to the demodulating unit 116, which demodulates the transmitting vector received from the DF detecting unit 114.
However, in such a conventional V-BLAST system, since all transmitting antennas use the same modulation system and power, high performance is achieved at the cost of a receiver having a complex structure.
Furthermore, in a receiver, a signal detection order for detecting a transmitting vector changes each time a channel is switched.